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Difficulty: MediumPopulation Dynamics and Ecological Sampling

An ecology student placed a 0.5 m20.5\text{ m}^2 quadrat 1010 times at random within a plot in Okomu National Park to estimate the population of Siam weed (*Chromolaena odorata*). If a total count of 120120 Siam weed plants was recorded across all sample throws, what is the estimated population density of Siam weed in plants per square metre?

  1. 24 plants/m224\text{ plants/m}^2Answer
  2. B
    240 plants/m2240\text{ plants/m}^2
  3. C
    12 plants/m212\text{ plants/m}^2
  4. D
    60 plants/m260\text{ plants/m}^2

Answer

The estimated population density of Siam weed is 24 plants/m224\text{ plants/m}^2.
To estimate population density per unit area using quadrat sampling, the total number of individuals counted (120120) must be divided by the total area of all quadrats combined (10×0.5 m2=5.0 m210 \times 0.5\text{ m}^2 = 5.0\text{ m}^2). Dividing 120120 by 5.0 m25.0\text{ m}^2 yields 24 plants/m224\text{ plants/m}^2.

Step-by-Step Solution

1
Calculate the total area sampled by the quadrat throws.
Total Sampled Area=Number of Throws×Area of One Quadrat=10×0.5 m2=5.0 m2\text{Total Sampled Area} = \text{Number of Throws} \times \text{Area of One Quadrat} = 10 \times 0.5\text{ m}^2 = 5.0\text{ m}^2
Population density must be calculated over the aggregate area covered by all sampling units combined.
2
Determine the population density per square metre.
Population Density=Total Number of OrganismsTotal Sampled Area=120 plants5.0 m2=24 plants/m2\text{Population Density} = \frac{\text{Total Number of Organisms}}{\text{Total Sampled Area}} = \frac{120\text{ plants}}{5.0\text{ m}^2} = 24\text{ plants/m}^2
Density measures the number of individuals per unit area.

Key Concept

Quadrat Population Density Calculation
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Topics

Population Dynamics and Ecological Sampling

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